The present invention relates to delivery chutes and in particular to a delivery chute for use in a sorting machine having a horizontal conveyor.
Horizontal conveyor sorting machines are well known and are described in such patents as U.S. Pat. Nos. 4,077,620, 4,147,252 and 4,527,792.
A particular use for such sorting machines is to sort pieces of mail, including mail referred to as "flats" which generally are envelopes and magazines having a large height and width as compared to their thickness.
In some such mail sorting machines there are up to 100 discharge outputs from the machine as the objects are sorted as they move along a horizontal conveyor. Two machines utilized in particular are referred to as the FSM881 and the FSM775 by the United States Postal Service.
Discharge chutes are provided on these sorting machines to guide the flat to a stationary container positioned below each discharge chute. The chutes, however, do not positively guide and orient the flat, but only provide a guided free fall of the flat after it has been diverted from the conveyor. The only constant is the entering velocity of the flat which is approximately 72 inches per second. Variables affecting the movement of the flat after it has been diverted from the conveyor include the weight, size, aspect ratio, static electricity, surface friction effects against the chute, stiffness of the flat and aerodynamic characteristics of the flat. Even the effects of humidity may change the coefficient of friction of the flat. Considering these variables, different trajectories and rotations occur along the chute path. The chute itself is a short spiral sheet, curving and descending along a vertical axis.
An intercepting diverter is provided at each discharge station, positioned near the bottom of the conveyor channel in which the flats are carried. Generally the diverter is positioned below transport push rods which push the individual flats along the fixed support surfaces of the conveyor. When the diverter is rotated in toward the feed path, the next flat is forced to turn through a small angle toward the guide chute. The diverter imparts a retarding force to the flat, and since the flat center of gravity generally is above the diverter, a torque is applied to the flat, beginning a rotation. A secondary effect occurs as the flat leaves the transport and moves off of the horizontal supporting surface of the conveyor. The leading edge of the flat is no longer supported, allowing it to fall and causing rotation of the flat. The rotational energy imparted to the flat is a function of the length of the flat, its weight and velocity. The analysis of rotation concludes that the significant parameter is the aspect ratio of the flat dimensions (height to length). Flats with small aspect ratios (height exceeding length) will have a smaller rotational velocity. This analysis assumes the center of gravity of the flat coincides with the center of area.
As the flat falls along the chute, its contact with the chute also affects the rotation of the flat, but probably in an indeterminate way, allowing for the variability of the flat characteristics. The curve in the chute increases the normal contact force due to centripetal effects, increasing drag and slowing the velocity of the flat. The aforementioned factors result generally in an unedged, disheveled stack of flats, many with loss of the original orientation on the transport path. The flats are discharged from the chute approximately 90.degree. from their direction of travel along the conveyor and are received in rectangular boxes which are set on the floor spaced laterally from the conveyor to accommodate the lateral movement of the flat moving along the chute and its airborne travel after leaving the chute. A distant edge of the box is required to be elevated to prevent or reduce over shooting of the box by the airborne flats.
It would be advantageous, therefore, to provide a transport chute which maintains the orientation of objects diverted from a horizontal conveyor such that all of the objects deposited into the output stack will have the same orientation to each other as they did on the horizontal conveyor.